Mobile station apparatus and method to perform a random access using a randomly selected signature in a cellular communication system

ABSTRACT

A mobile station apparatus detects a signature not reserved as a dedicated signature informed by a base station. In addition, the mobile station apparatus performs a random access using a randomly selected signature, in case of detecting a signature not reserved as a dedicated signature.

This application is a Continuation of U.S. application Ser. No.16/168,579, filed on Oct. 23, 2018, which is a Divisional of U.S.application Ser. No. 14/678,498, filed on Apr. 3, 2015, now U.S. Pat.No. 10,123,354, issued on Nov. 6, 2018, which is a Continuation of U.S.application Ser. No. 14/050,116, filed on Oct. 9, 2013, now U.S. Pat.No. 9,042,307, issued on May 26, 2015, which is a Divisional ofapplication Ser. No. 12/593,884 filed on Sep. 29, 2009, now U.S. Pat.No. 8,588,134, issued Nov. 19, 2013, and for which priority is claimedunder 35 U.S.C. § 120. Application Ser. No. 12/593,884 is the nationalphase of PCT International Application No. PCT/JP2008/060184 filed onJun. 3, 2008, under 35 U.S.C. § 371, which claims the benefit ofpriority of JP 2008-021557, filed on Jan. 31, 2008, and JP 2007-15099filed on Jun. 6, 2007. The entire contents of each of theabove-identified applications are hereby incorporated by reference.

TECHNICAL FIELD

The present invention relates to a mobile communication system, a basestation apparatus and a mobile station apparatus employing the cellularcommunication system.

BACKGROUND ART

In the 3GPP (3rd Generation Partnership Project), W-CDMA has beenstandardized as the 3rd generation cellular mobile communication systemat present and the service has successively started. Furthermore, HSDPA(High Speed Downlink Packet Access) with a higher communication speedhas been standardized and the service is to be started.

On the other hand, in the 3GPP, evolution of the 3rd generation radioaccess (Evolved Universal Terrestrial Radio Access; hereinafter referredto as the EUTRA) is being examined. As a downlink of the EUTRA, OFDM(Orthogonal Frequency Division Multiplexing) has been proposed. Also, asan uplink of the EUTRA, a single carrier communication system of DFT(Discrete Fourier Transform)-spread OFDM has been proposed.

The uplink of the EUTRA includes, as illustrated in FIG. 17 , an UplinkPilot Channel UPiCH, a Random Access Channel RACH, an Uplink SharedChannel UL-SCH and a Physical Uplink Control Channel PUCCH.

The downlink of the EUTRA includes, as illustrated in FIG. 17 , aDownlink Pilot Channel DPiCH, a Downlink Synchronization Channel DSCH, aCommon Control Physical Channel CCPCH, a Physical Downlink ControlChannel PDCCH (L1/L2 (Layer 1/Layer 2) control channel), aDownlink-Shared Channel DL-SCH) (see, for example, Non-patent Document1).

In the OFDM communication system, signals transmitted from each of aplurality or mobile stations to a base station are demodulated in abatch, and therefore, it is necessary to control arrival time of signalsreaching from respective mobile stations to the base station to beconstant. Although interference derived from delay can be prevented inthe OFDM communication system by providing a guard interval (of, forexample, 5 microseconds with a subcarrier of 15 kHz and an OFDM symbolof 70 microseconds), the interference cannot be avoided if the timing isshifted beyond the guard interval.

A random access channel, using a minimum unit of a 1.25 MHz band, isconstituted so as to cope with a large number of accesses by, forexample, preparing a plurality of access channels as illustrated in FIG.18 .

FIG. 18 is a diagram illustrating an exemplary assignment on radioresources of a random access channel RACH, an uplink shared channelUL-SCH, an uplink pilot channel UPiCH and a physical uplink controlchannel PUCCH. In FIG. 18 , the abscissa indicates the time and theordinate indicates the frequency. Also, FIG. 18 illustrates thestructure of one radio frame, and the radio frame is divided into aplurality of radio resources. In this exemplary structure, each radioresource is constituted as a unit area of 1.25 MHz in the frequencydirection and 1 ms in the time direction, and the random access channelRACH and the uplink shared channel UL-SCH of FIG. 17 are allocated tothese areas as illustrated in FIG. 18 . In this manner, the randomaccess channel RACH uses the 1.25 MHz band as the minimum unit.Incidentally, in FIG. 18 , the uplink pilot channel UPiCH is allocateddispersedly in the areas of the uplink shared channel UL-SCH withrespect to each symbol or subcarrier.

The random access channel is used for the principal purpose of attainingsynchronization between a mobile station apparatus (hereinafter referredto as the “mobile station”) and a base station apparatus (hereinafterreferred to as the “base station”). Furthermore, consideration is madefor transmitting information of several bits such as a request forscheduling of allocating a radio resource to reduce connect time betweenthe mobile station and the base station (see, for example, Non-PatentDocument 2).

In a random access, a preamble alone is transmitted for attainingsynchronization. The preamble includes a signature corresponding asignal pattern representing information, and information of several bitscan be specified by preparing several tens kinds of signatures. Atpresent, transmission of 6-bit information is assumed and preparation of64 kinds of signatures is assumed.

It is assumed that a random ID is allocated to 5 bits of 6-bitinformation and that information such as a reason for the random accessand a path loss/CQI (Channel Quality Indicator) of the downlink isallocated to the remaining 1 bit (see, for example, Non-Patent Document3).

FIG. 19 is a sequence chart used for explaining an exemplary procedureof a conventional random access. In the procedure of the conventionalrandom access, as illustrated in FIG. 19 , a mobile station firstselects a signature on the basis of a random ID, a reason for the randomaccess and path loss/CQI information at the downlink (step (hereinaftershortened as “ST”). Then, a preamble including the selected signature(that is, a random access preamble) is transmitted by using a randomaccess channel (ST1902: Message 1).

When a base station receives the preamble from the mobile station, itcalculates, on the basis of the preamble, synchronization timing shiftbetween the mobile station and the base station and performs schedulingfor transmitting an L2/L3 (Layer 2/Layer 3) message (ST1903).Thereafter, when it is found from the reason for the random access thatthe mobile station needs C-RNTI (Cell-Radio Network Temporary Identity),the base station allocates C-RNTI to the mobile station, and transmits arandom access response including synchronization timing shiftinformation (synchronization information), scheduling information, asignature ID number and the C-RNTI (ST1904: Message 2).

When the mobile station receives these information from the basestation, it extracts a response from the base station including thetransmitted signature ID number (ST1905). Then, the mobile stationtransmits an L2/L3 message by using a radio resource scheduled by thebase station (ST1906: Message 3). When the base station receives theL2/L3 message from the mobile station, it transmits contentionresolution for determining whether or not contention has occurred withanother mobile station (ST1907: Message 4) (see, for example, Non-PatentDocument 3).

A problem of such a random access is occurrence of contention causedwhen a plurality of different mobile stations select the same signatureand the same random access channel. When a plurality of mobile stationsselect the same signature and perform transmission by using a radioresource block having the same time and frequency, namely, by using thesame random access channel, contention occurs in the preamble (ST1902)of FIG. 19 .

When the base station cannot detect the preamble (ST1902) due to suchcontention, it cannot transmit the response (ST1904) including thesynchronization information and the like. In this case, since the mobilestation cannot receive the response (ST1904) from the base station, itshould perform a random access again by selecting a signature and arandom access channel after a prescribed time.

On the other hand, if when the base station can detect the preamble(ST1902), the base station performs the scheduling of an L2/L3 messageand calculates the synchronization timing shift for transmitting theresponse (ST1904) to the mobile station. However, the plural mobilestations receive the response (ST1904) from the base station. Therefore,the plural mobile stations transmit the L2/L3 message (ST1906) by usingthe scheduled radio resource, resulting in causing contention in theL2/L3 message (ST1906).

When the base station cannot detect the L2/L3 message (ST1906) due tosuch contention, it cannot transmit the response (ST1907). In this case,since the mobile station cannot receive the response (ST1907) from thebase station, it should perform a random access again by selecting asignature and a random access channel after a prescribed time. In thismanner, in the case where a plurality of mobile stations select the samesignature and random access channel, contention may occur, and when thecontention occurs, it takes time elapsing up to ST1907 of FIG. 19 atmost to detect the contention.

On the other hand, in transmission of a downlink-shared channel DL-SCH,HARQ (Hybrid Automatic Repeat Request) is employed. In the HARQ, afterdecoding the DL-SCH in a mobile station, ACK (Acknowledgement) is fedback to the base station when CRC (Cyclic Redundancy Check) succeeds andHACK (Negative Acknowledgement) is fed back to the base station when theCRC fails, and thus, the base station determines whether or notretransmission is to be performed. This ACK/HACK is transmitted by usinga physical ink control channel PUCCH immediately after receiving theDL-SCH. The mobile station receives the downlink-shared channel DL-SCHafter receiving the physical downlink control channel PDCCH, andtransmits the ACK when the CRC succeeds.

Incidentally, in the case where the mobile station and the base stationare out of uplink synchronization with each other (for example, in thecase of a DRX state where data transmission has not been performed for along period of time and the mobile station has been monitoring, a signalfor allocating a downlink resource on a long cycle), when downlink datatransmission from the base station is resumed, the mobile station cannottransmit the HARQ ACK/HACK (Hybrid Automatic Repeat RequestAcknowledgement/Negative Acknowledgement) by using a PUCCH. This isbecause since it is out of uplink synchronization, if the HARQ ACK/NACKis transmitted, it causes interference with another mobile station.According in resuming the downlink data transmission, it is necessary toattain uplink synchronization through a random access.

In this case, contention cannot be avoided because a random access isperformed, and it is apprehended that it may take a long time to resumethe downlink data transmission. In order to avoid such a problem, aproposal for preventing contention in a random access performed forresuming downlink data transmission by using a signature for resumingthe downlink data transmission has been made (see, for example,Non-Patent Document 4). At this point, the procedure for resumingdownlink data transmission proposed in Non-Patent Document 4 will bedescribed with reference to FIG. 20 .

When it is determined to resume downlink data transmission to a mobilestation out of uplink synchronization, a base station transmits anuplink synchronization request to the mobile station as illustrated inFIG. 20 (ST2001). The uplink synchronization request is transmitted byusing an L1/L2 (layer 1/Layer 2) physical downlink control channelPDCCH. The uplink synchronization request includes a signature ID numberof a random access to be sent from the mobile station. In the followingdescription, this is designated as a dedicated signature.

When the uplink synchronization request is received from the basestation, the mobile station transmits a preamble (a random accesspreamble) including the dedicated signature received in the uplinksynchronization request by using a random access channel to the basestation (ST2002). When the preamble including the dedicated signature isreceived from the mobile station, the base station transmits a TA(Timing Advance) command corresponding to a synchronization timing shiftto the mobile station as a response (a preamble response) to the randomaccess (ST2003).

After transmitting the TA command, the base station transmits an L1/L2control channel including downlink resource a location to the mobilestation (ST2004). Subsequently, the base station transmits downlink datato the mobile station (ST2005).

Non-Patent Document 1: R1-050850 “Physical Channel and Multiplexing inEvolved UTRA Uplink”, 3GPP TSG RAN WG1 Meeting #42 London, UK, Aug.29-Sep. 2, 2005

Non-Patent Document 2: 3GPP TR (Technical Report) 25.814, V7.0.0(2006-06), Physical layer aspects for evolved Universal TerrestrialRadio Access (UTRA)

Non-Patent Document 3: 3GPP TS (Technical Specification) 36.300, VO. 90(2007-03), Evolved Universal Terrestrial Radio Access (E-UTRA) andEvolved Universal Terrestrial Radio Access Network (E-UTRAN), Overalldescription Stage 2

Non-Patent Document 4: R2-062165 “UL Synchronization”, 3GPP TSG RAN WG2Meeting #54 Tallinn, 28 Aug.-1 Sep. 2006

DISCLOSURE OF THE INVENTION Problem to be Solved the Invention

In resuming the downlink data transmission, however, althoughtransmission of a dedicated signature included in an L1/L2 controlchannel is being examined, if there are not sufficient allocatablededicated signatures, an uplink synchronization request cannot betransmitted. As a result, when a dedicated signature cannot beallocated, there arises a problem that the L1/L2 control channel isuselessly used. Such a problem arises similarly not only when, forexample, continuation of uplink synchronization is managed with a timerin both a base station and a mobile station but also when a base stationdetects that a mobile station is out of uplink synchronization.

The present invention was devised in consideration of such a problem,and an object of the invention is providing a mobile communicationsystem, a base station apparatus and a mobile station apparatus in whichan efficient procedure can be realized when a mob e station is out ofuplink synchronization, no matter whether a dedicated signature can beallocated.

Means for Solving the Problem

(1) In order to achieve the object, the present invention provides thefollowing means: The mobile station apparatus of this invention managesuplink synchronization and performs a random access in detecting anuplink or downlink resource allocation when out of uplinksynchronization.

The uplink synchronization is thus managed, and when the mobile stationapparatus is out of uplink synchronization and uplink or downlinkresource allocation is detected, a random access performed, andtherefore, base station apparatus can efficiently instruct the mobilestation apparatus to perform a random access through a simple operation.

(2) Alternatively, the mobile station apparatus of this inventionperforms a random access by using a dedicated signature in detecting thededicated signature and performs a random access by using a randomlyselected signature in detecting a signature not reserved as a dedicatedsignature.

In this manner, a random access is performed by using a dedicatedsignature in detecting the dedicated signature and a random access isperformed by using a randomly selected signature in detecting asignature not reserved as a dedicated signature, and therefore, a basestation apparatus can efficiently instruct the mobile station apparatusto perform a random access through a simple operation.

(3) Alternatively, the mobile communication system of this inventionincludes a base station apparatus and a mobile station apparatus, thebase station apparatus allocates an uplink or downlink resourceallocation to the mobile station apparatus, and the mobile stationapparatus manages uplink synchronization and performs a random access indetecting or downlink resource allocation when out of uplinksynchronization.

In this manner, the base station apparatus allocates an uplink ordownlink resource allocation to the mobile station apparatus and themobile station apparatus manages uplink synchronization, and when themobile station apparatus is out of uplink synchronization and uplink ordownlink resource allocation is detected, a random access is performed.Therefore, the base station apparatus can efficiently instruct themobile station apparatus to perform a random access through a simpleoperation.

(4) Alternatively, the mobile communication system of this inventionincludes a base station apparatus and a mobile station apparatus, thebase station apparatus specifies a signature for the mobile stationapparatus, and the mobile station apparatus performs a random access byusing a dedicated signature in detecting the dedicated signature andperforms a random access by using a randomly selected signature indetecting a signature not reserved as a dedicated signature.

In this manner, the base station apparatus specifies a signature for themobile station apparatus, and the mobile station apparatus performs arandom access by using a dedicated signature when the dedicatedsignature is detected, and performs a random access by using a randomlyselected signature when a signature not reserved as a dedicatedsignature is detected. Therefore, the base station apparatus canefficiently instruct the mobile station apparatus to perform a randomaccess through a simple operation.

(5) Alternatively, the mobile communication system of this inventionincludes a base station apparatus transmitting a DL-SCH to a mobilestation apparatus, the mobile station apparatus performs a random accessby using a different signature depending upon information included inthe DL-SCH and a result of CRC of the DL-SCH, and the base stationapparatus transmits downlink data after determining whether or notcontention resolution is to be transmitted depending upon the signatureused in the random access.

In this manner, the mobile station apparatus performs a random access byusing a different signature depending upon information included in theDL-SCH and a result of CRC of the DL-SCH, and the base station apparatustransmits downlink data after determining whether or not contentionresolution is to be transmitted depending upon the signature used in therandom access. Therefore, since downlink data transmission can beresumed in accordance with the signature selected by the mobile stationapparatus while assuming occurrence of contention with another mobilestation apparatus, an efficient procedure can be realized in resumingdownlink data transmission, for example, no matter whether a dedicatedsignature can be allocated. Also in uplink resynchronization, anefficient procedure can be realized, for example, no matter whether adedicated signature for uplink resynchronization can be allocated.

(6) In the mobile communication system of this invention, the mobilestation apparatus receives the DL-SCH including information forspecifying a dedicated signature used for resuming downlink datatransmission, and performs a random access by using the dedicatedsignature when the CRC of the DL-SCH succeeds, and the base stationapparatus transmits the downlink data without transmitting thecontention resolution.

In this manner, when the mobile station apparatus performs a randomaccess by using a dedicated signature, downlink data is transmittedwithout transmitting contention resolution, and therefore, an efficientprocedure can be realized when a dedicated signature can be allocated inresuming downlink data transmission.

(7) In the mobile communication system of this invention, the mobilestation apparatus receives the DL-SCH including information forspecifying a dedicated signature used for resuming downlink datatransmission, and performs a random access by using a randomly selectedsignature when the CRC of the DL-SCH fails, and the base stationapparatus transmits the downlink data after transmitting the contentionresolution.

In this manner, when the mobile station apparatus performs a randomaccess by using a randomly selected signature, downlink data istransmitted after transmitting contention resolution. Therefore, evenwhen a dedicated signature cannot be allocated in resuming downlink datatransmission, an efficient procedure can be realized in consideration ofcontention with another mobile station apparatus.

(8) In the mobile communication system of this invention, the mobilestation apparatus manages uplink synchronization, and performs a randomaccess by using a randomly selected signature in receiving the DL-SCHnot including information for specifying a dedicated signature used forresuming downlink data transmission when out of unlink synchronization,and the base station apparatus transmits the downlink data aftertransmitting the contention resolution.

In this manner, when the mobile station apparatus performs a randomaccess by using a randomly selected signature, downlink data istransmitted after transmitting contention resolution. Therefore, evenwhen a dedicated signature cannot be allocated in resuming downlink datatransmission, an efficient procedure can be realized in consideration ofcontention with another mobile station apparatus.

(9) In the mobile communication system of this invention, the basestation apparatus instructs to perform a random access by using arandomly selected signature by not transmitting the DL-SCH.

In this manner, a random access using a randomly selected signature isinstructed to be performed by not transmitting a DL-SCH, and therefore,a random access using a randomly selected signature can be instructed tobe performed without using a downlink resource.

(10) In the mobile communication system of this invention, the mobilestation apparatus receives the DL-SCH including an uplinksynchronization request and information for specifying a dedicatedsignature for uplink resynchronization, and performs a random access byusing the dedicated signature for the uplink resynchronization when theCRC of the DL-SCH succeeds, and the base station apparatus transmits thedownlink data without transmitting the contention resolution.

In this manner, when the mobile station apparatus performs a randomaccess by using a dedicated signature for uplink resynchronization,downlink data is transmitted without transmitting contention resolution,and therefore, an efficient procedure can be realized when a dedicatedsignature for uplink resynchronization can be allocated for uplinkresynchronization. In particular, when the mobile station apparatusreceives a DL-SCH including an uplink synchronization request from thebase station apparatus, the mobile station apparatus performs a randomaccess by using the dedicated signature for uplink resynchronization.Therefore, even when the mobile station apparatus does not recognizethat it is out of uplink synchronization, the uplink resynchronizationcan be attained.

(11) In the mobile communication system of this invention, the mobilestation apparatus performs a random access by using a randomly selectedsignature in receiving the DL-SCH including an uplink synchronizationrequest but not including information for specifying a dedicatedsignature for uplink resynchronization, and the base station apparatustransmits the downlink data after transmitting the contentionresolution.

In this manner, when the mobile station apparatus performs a randomaccess by using a randomly selected signature, downlink data istransmitted after transmitting contention resolution. Therefore, evenwhen a dedicated signature for uplink resynchronization cannot beallocated for uplink resynchronization, an efficient procedure can berealized in consideration of contention with another mobile stationapparatus. In particular, when the mobile station apparatus receives aDL-SCH including an uplink synchronization request from the base stationapparatus, the mobile station apparatus performs a random access byusing a randomly selected signature, and therefore, even when the mobilestation apparatus does not recognize that it is out of uplinksynchronization, the uplink resynchronization can be attained.

(12) The base station apparatus of this invention that transmits aDL-SCH to a mobile station out of uplink synchronization, includestransmitting means for transmitting a DL-SCH including information of adedicated signature for resuming downlink data transmission; andcontrolling means for determining whether or not contention resolutionis to be transmitted depending upon a signature used in a random accessperformed by the mobile station apparatus.

In this manner, since it is determined whether or not contentionresolution is to be transmitted depending upon the signature used in therandom access performed by the mobile station apparatus, downlink datatransmission can be resumed, while assuming occurrence of contention, inaccordance with the signature selected by the mobile station apparatus.Therefore, an efficient procedure can be realized in resuming downlinkdata transmission no matter whether, for example, a dedicated signaturefor resuming downlink data transmission can be allocated.

(13) In the base station apparatus of this invention, the transmittingmeans transmits a DL-SCH including information for specifying thededicated signature, and the controlling means does not transmit thecontention resolution in detecting a random access performed by usingthe dedicated signature.

In this manner, when a random access performed by using a dedicatedsignature is accepted from a mobile station apparatus, contentionresolution is not transmitted, and therefore, an efficient procedure canbe realized when a dedicated signature can be allocated in resumingdownlink data transmission.

(14) In the base station apparatus of this invention, the transmittingmeans transmits a DL-SCH including information for specifying thededicated signature, and the controlling means transmits the contentionresolution in detecting a random access performed by using a randomlyselected signature.

In this manner, when a random access performed by using a randomlyselected signature is accepted from a mobile station apparatus,contention resolution is transmitted. Therefore, even when a dedicatedsignature cannot be allocated in resuming downlink data transmission, anefficient procedure can be realized in consideration of contention withanother mobile station apparatus.

(15) In the base station apparatus of this invention, the transmittingmeans transmits a DL-SCH not including information for specifying thededicated signature, and the controlling means transmits the contentionresolution in detecting a random access performed by using a randomlyselected signature.

In this manner, when a random access performed by using a randomlyselected signature is accepted from a mobile station apparatus,contention resolution is transmitted. Therefore, even when a dedicatedsignature cannot be allocated in resuming downlink data transmission, anefficient procedure can be realized in consideration of contention withanother mobile station apparatus.

(16) In the base station apparatus of this invention, the transmittingmeans instructs to perform a random access by using a randomly selectedsignature by not transmitting the DL-SCH.

In this manner since a random access using a randomly selected signatureis instructed to be performed by not transmitting a DL-SCH, a randomaccess using a randomly selected signature can be instructed to beperformed without using a downlink resource.

(17) The base station apparatus of this invention that transmits aDL-SCH to a mobile station apparatus out of uplink synchronization,includes transmitting means for transmitting a DL-SCH including anuplink synchronization request and formation of a dedicated signaturefor uplink resynchronization.

In this manner, since a DL-SCH including synchronization request andinformation of a dedicated signature for uplink resynchronization istransmitted to a mobile station apparatus of uplink synchronization, theuplink synchronization request and the information of the dedicatedsignature for uplink resynchronization can be transmitted during thecommunication.

(18) The mobile station apparatus of this invention that receives aDL-SCH from a base station apparatus, includes discriminating means fordiscriminating information included in the DL-SCH and a CRC result ofthe DL-SCH; and random access executing means for performing a randomaccess by using a different signature depending upon a discriminationresult obtained by the discriminating means.

In this manner, since a random access is performed by using a differentsignature depending upon information included in the DL-SCH and adiscrimination result of the CRC of the DL-SCH, the base stationapparatus can resume downlink data transmission while assumingcontention, for example, depending upon the signature used in the randomaccess, and therefore, an efficient procedure can be realized inresuming downlink data transmission no matter whether a dedicatedsignature for resuming downlink data transmission can be allocated.Furthermore, since the base station apparatus can attain uplinkresynchronization while assuming occurrence of contention depending upona signature used in the random access, an efficient procedure can berealized in the uplink resynchronization no matter whether a dedicatedsignature for uplink resynchronization can be allocated.

(19) In the mobile station apparatus of this invention, the mobilestation apparatus manages uplink synchronization, and when the mobilestation apparatus is out of uplink synchronization and thediscriminating means discriminates that the DL-SCH includes informationfor specifying a dedicated signature for resuming downlink datatransmission and that the CRC result of the DL-SCH is successful, therandom access executing means performs a random access by using thededicated signature.

In this manner, when it is discriminated that the DL-SCH includesinformation for specifying a dedicated signature for resuming downlinkdata transmission and that the CRC result of the DL-SCH is successful, arandom access is performed by using the dedicated signature. Therefore,when a dedicated signature can be allocated in resuming downlink datatransmission, an efficient procedure can be realized by, for example,transmitting, from a base station apparatus, downlink data withouttransmitting contention resolution in accordance with the random accessperformed by using the dedicated signature.

(20) In the mobile station apparatus of this invention, the mobilestation apparatus manages uplink synchronization and when the mobilestation apparatus is out of uplink synchronization and thediscriminating means discriminates that the CRC result of the DL-SCH isunsuccessful, the random access executing means performs a random accessby using a randomly selected signature.

In this manner, a random access is performed by using a randomlyselected signature when the CRC result of the DL-SCH is discriminated tobe unsuccessful, and therefore, even when a dedicated signature cannotbe allocated in resuming downlink data transmission, an efficientprocedure can be realized in consideration of contention with anothermobile station apparatus by, for example, transmitting, from a basestation apparatus, downlink data after transmitting contentionresolution in accordance with the random access performed by using therandomly selected signature.

(21) In the mobile station apparatus of this invention, the mobilestation apparatus manages uplink synchronization, and when the mobilestation apparatus is out of uplink synchronization and thediscriminating means discriminates that the DL-SCH does not includeinformation for specifying a dedicated signature for resuming downlinkdata transmission, the random access executing means performs a randomaccess by using a randomly selected signature.

In this manner, a random access is performed by using a randomlyselected signature when the DL-SCH is discriminated not to includeinformation for specifying a dedicated signature, and therefore, evenwhen a dedicated signature cannot be allocated in resuming downlink datatransmission, an efficient procedure can be realized in consideration ofcontention with another mobile station apparatus by, for example,transmitting, from a base station apparatus, downlink data aftertransmitting contention resolution in accordance with the random accessperformed by using the randomly selected signature.

(22) In the mobile station apparatus of this invention, when thediscriminating means discriminates that the CRC result of the DL-SCH issuccessful and that the DL-SCH includes an uplink synchronizationrequest and information for specifying a dedicated signature for uplinkresynchronization, the random access executing means performs a randomaccess by using the dedicated signature for uplink resynchronization.

In this manner, when it is discriminated that the DL-SCH includes anunlink synchronization request and information for specifying adedicated signature for uplink resynchronization and that the CRC resultof the DL-SCH is successful, a random access is performed by using thededicated signature for the uplink resynchronization. Therefore, anefficient procedure can be realized when a dedicated signature foruplink resynchronization can be allocated for the uplinkresynchronization by, for example, transmitting, from a base stationapparatus, downlink data without transmitting contention resolution inaccordance with the random access performed by using the dedicatedsignature. In particular, a random access is performed when it isdiscriminated that the DL-SCH includes an uplink synchronizationrequest, and therefore, even when the mobile station apparatus does notrecognize that it is out of uplink synchronization, the uplinkresynchronization can be attained.

(23) In the mobile station apparatus of this invention, when thediscriminating means discriminates that the DL-SCH includes an uplinksynchronization request but does not include information for specifyinga dedicated signature for uplink resynchronization, the random accessexecuting means performs a random access by using a randomly selectedsignature.

In this manner, when it is discriminated that the DL-SCH includes anuplink synchronization request but does not include information forspecifying a dedicated signature for uplink resynchronization, a randomaccess is performed by using a randomly selected signature. Therefore,even when a dedicated signature for uplink resynchronization cannot beallocated for uplink resynchronization, an efficient procedure can berealized in consideration of contention with another mobile stationapparatus by, for example, transmitting, from a base station apparatus,downlink data after transmitting contention resolution in accordancewith the random access performed, by using the randomly selectedsignature. In particular, a random access is performed when it isdiscriminated that the DL-SCH includes an uplink synchronizationrequest, and therefore, even when the mobile station apparatus does notrecognize that it is out of uplink synchronization, the uplinkresynchronization can be attained.

Effects of the Invention

According to the present invention, it is possible to resume downlinkdata transmission and attain uplink resynchronization in accordance witha signature selected by a mobile station apparatus while assumingoccurrence of contention with another mobile station apparatus, andtherefore, an effective procedure can be realized when a mobile stationis out of uplink synchronization, no matter whether a dedicatedsignature can be allocated.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram illustrating an exemplary configuration of abase station included in a communication system according to anembodiment of the invention.

FIG. 2 is a block diagram illustrating an exemplary configuration of amobile station included in the communication system of the embodiment.

FIG. 3 is a sequence chart illustrating an operation performed when thebase station of the embodiment transmits a dedicated signature by usinga DL-SCH and the mobile station succeeds in CRC of the DL-SCH.

FIG. 4 is a sequence chart illustrating an operation performed when thebase station of the embodiment transmits a dedicated signature by usinga DL-SCH and the mobile station fails in the CRC of the DL-SCH.

FIG. 5 is a sequence chart illustrating an operation performed when thebase station of the embodiment does not transmit a dedicated signatureby using a DL-SCH.

FIG. 6 is a sequence chart illustrating an operation performed when thebase station of the embodiment does not transmit a DL-SCH.

FIG. 7 is a sequence chart illustrating an operation performed when themobile station of the embodiment fails in the CRC of an L1/L2 controlchannel.

FIG. 8 is a flowchart used for explaining an operation performed by thebase station of the embodiment for resuming downlink data transmissionto a mobile station out of uplink synchronization.

FIG. 9 is a flowchart used for explaining an operation performed by thebase station of the embodiment for random access control.

FIG. 10 is a flowchart used for explaining an operation performed by themobile station out of uplink synchronization of the embodiment forresuming downlink data transmission.

FIG. 11 is a sequence chart illustrating an operation performed when thebase station of the embodiment transmits an uplink synchronizationrequest and a dedicated signature by using a DL-SCH and the mobilestation succeeds in the CRC of the DL-SCH.

FIG. 12 is a sequence chart illustrating an operation performed when thebase station of the embodiment transmits an uplink synchronizationrequest by using a DL-SCH and the mobile station fails in the CRC of theDL-SCH.

FIG. 13 is a sequence chart illustrating an operation performed when thebase station of the embodiment transmits an uplink synchronizationrequest by using a DL-SCH.

FIG. 14 is a flowchart used for explaining an operation performed by themobile station of this embodiment for uplink resynchronization.

FIG. 15 is a flowchart used for explaining operations performed by themobile station of the embodiment when continuation of uplinksynchronization is managed with a timer and when an uplinksynchronization request from the base station is received.

FIG. 16 is a block diagram illustrating an exemplary configuration of apart of an upper layer of the mobile station of the embodiment.

FIG. 17 is a diagram explaining the structure of uplink/downlink of theEUTRA.

FIG. 18 is a diagram explaining a random access channel of the uplink ofthe EUTRA.

FIG. 19 is a sequence chart used for explaining an exemplary procedureof a conventional random access.

FIG. 20 is a sequence chart used for explaining an exemplaryconventional procedure for resuming downlink data transmission.

DESCRIPTION OF REFERENCE NUMERALS

100 base station apparatus (base station)

101 data control unit

102 OFDM modulation unit

103 scheduling unit

104 radio unit

105 channel estimation unit

106 DFT-S-OFDM demodulation unit

107 control data extraction unit

108 preamble detection unit

109 signature management unit

200 mobile station apparatus (mobile station)

201 data control unit

202 DFT-S-OFDM modulation unit

203 scheduling unit

204 signature selection unit

205 preamble generation unit

206 synchronization correction unit

207 radio unit

208 channel estimation unit

209 OFDM demodulation unit

210 control data extraction unit

1601 uplink synchronization management unit

1602 CRC result discrimination unit

1603 random access execution unit

1604 random access discrimination unit

BEST MODE FOR CARRYING OUT THE INVENTION

A preferred embodiment of the invention will now be described withreference to the accompanying drawings. At this point, a random accesschannel RACH and the content of a preamble corresponding to theprerequisite of the description of a mobile communication system(hereinafter sometimes referred to as the “communication system”)according to an embodiment of the invention will be briefly described. Arandom access channel RACH is a channel having a guard time (of, forexample, 97 microseconds) and usable by a mobile station apparatus(hereinafter sometimes referred to as a “mobile station”) out ofsynchronization. A preamble (with a preamble length of, for example, 0.8ms) is selectable from 64 signatures, and a mobile station selects oneof the 64 signatures and transmits it to a base station apparatus(hereinafter sometimes referred to as a “base station”). When a basestation receives a random access preamble from a mobile station, itdetects a shift between arrival time of the preamble and a base time.The granularity of timing shift information is, for example, 0.52microsecond.

In the communication system of this embodiment, when downlink datatransmission to a mobile station out of uplink synchronization isresumed, a base station transmits downlink resource allocation by usingan L1/L2 physical downlink control channel PDCCH and transmits downlinkdata and a signature to be used for resuming transmission of downlinkdata (hereinafter referred to as the “dedicated signature”) by usingdownlink-shared channel (hereinafter referred to as the “DL-SCH”). WhenCRC (Cyclic Redundancy Check) of the DL-SCH does not succeed, the mobilestation transmits an RACH indicating that there is contention withanother mobile station. On the other hand, when the CRC of the DL-SCHsucceeds, the mobile station transmits an RACH indicating that there isno contention with another mobile station by using the dedicatedsignature included in an L2/L3 message included in the DL-SCH.

The configurations of a base station and a mobile station included inthe communication system of this embodiment will now be described. FIG.1 is a block diagram illustrating an exemplary configuration of the basestation included in the communication system of this embodiment. FIG. 2is a block diagram illustrating an exemplary configuration of the mobilestation included in the communication system of this embodiment.

As illustrated in FIG. 1 , the base station 100 includes a data controlunit 101, an OFDM modulation unit 102, a scheduling unit 103, a radiounit 104, a channel estimation unit 105, a DFT-Spread-OFDM demodulationunit (DFT-S-OFDM demodulation unit) 106, a control data extraction unit107, a preamble detection unit 108 and a signature management unit 109.

The data control unit 101 accepts input of control data and user data,maps the control data, in accordance with an instruction issued by thescheduling unit 103, in a downlink common control physical channel, adownlink synchronization channel, a downlink pilot channel and aphysical downlink control channel, and maps transmission data (userdata) for each mobile station in a shared data channel.

The OFDM modulation unit 102 performs OFDM signal processing such asdata modulation, serial/parallel conversion of an input signal, IFFT(Inverse Fast Fourier Transform), CP (Cyclic Prefix) insertion andfiltering, so as to generate an OFDM signal.

The scheduling unit 103 includes a DL scheduling unit 103 a thatperforms scheduling of downlink and a UL scheduling unit 103 b thatperforms scheduling of uplink. The DL scheduling unit 103 a performsscheduling for mapping the user data in respective channels of thedownlink based on CQI information supplied by a mobile station and datainformation of each user supplied from an upper layer. The UL schedulingunit 103 b performs scheduling for mapping the user data in respectivechannels of the uplink based on an estimation result of radiopropagation path of the uplink supplied by the channel estimation unit105 and a resource allocation request issued by the mobile station.

The radio unit 104 upconverts OFDM modulated data to a radio frequencyand transmits the resultant to the mobile station. Also, the radio unit104 receives uplink data from the mobile station, downconverts it to abase band signal, and outputs the received data to the channelestimation unit 105, the DFT-S-OFDM demodulation unit 106 and thepreamble detection unit 108.

The channel estimation unit 105 estimates a radio propagator pathcharacteristic based on an uplink pilot channel UPiCH and outputs theestimation result to the DFT-S-OFDM demodulation unit 106. Also, thechannel estimation unit 105 outputs the estimation result of the radiopropagation path to the scheduling unit 103 for the scheduling of theuplink. Incidentally, the communication system of the unlink is hereinassumed to be a single charier system such as DFT-S-OFDM but may be amulticarrier system such as OFDM.

The DFT-S-OFDM demodulation unit 106 demodulates the received data inputfrom the radio unit 104 in accordance with the estimation result of theradio propagation path supplied from the channel estimation unit 105.The control data extraction unit 107 separates the received data to userdata (of an uplink shared channel UL-SCH) and control data (of aphysical uplink control channel PUCCH). Then, the control dataextraction unit 107 outputs CQI information of the downlink, out of theseparated control data, to the scheduling unit 103 and outputs the othercontrol data and the user data to the upper layer.

The preamble detection unit 108 detects a preamble, calculatessynchronization timing shift and reports a signature ID number and thesynchronization timing shift to the upper layer. At this point, when thesignature ID number accords with a signature informed by the signaturemanagement unit 109, a dedicated signature flag is set to “1”, and whenit is a signature not informed by the signature management unit 109, thededicated signature flag is set to “0”. Furthermore, when the signatureID number accords with the signature informed by the signaturemanagement unit 109, the preamble detection unit 108 reports to theupper layer that the preamble of the signature ID number informed by thesignature management unit 109 has been detected.

The signature management unit 109 selects a signature in accordance withan instruction issued by the upper layer, and forms the upper layer ofthe ID number (the signature ID number) of the selected signature.Furthermore, the signature management unit 109 informs the preambledetection unit 108 of the selected signature. Incidentally the signaturemanagement 109 checks signature ID numbers currently used and selects asignature from signatures excluding those used. The signature managementunit 109 stores the selected signature ID number and deletes thesignature detected by the preamble detection unit 108 from a storedcontent.

The base station 100 having the aforementioned configuration iscontrolled by the upper layer so as to execute processing throughprocedures illustrated in FIGS. 3 through 9 described later.

On the other hand, the mobile station 200 includes, as illustrated inFIG. 2 , a data control unit 201, a DFT-S-OFDM modulation unit 202, ascheduling unit 203, a signature selection unit 204, a preamblegeneration unit 205, a synchronization correction unit 206, a radio unit207, a channel estimation unit 208, an OFDM demodulation unit 209 and acontrol data extraction unit 210.

The data control unit 201 accepts input of user data and control dataand maps these data in an uplink scheduling channel in accordance withan instruction issued by the scheduling unit 203. The DFT-S-OFDMmodulation unit 202 performs data modulation and DFT-S-OFDM signalprocessing such as DFT conversion, subcarrier mapping, IFFT conversion,CP (Cyclic Prefix) insertion and filtering, so as to generate aDFT-Spread-OFDM signal. Incidentally, the communication system of theuplink is herein assumed to be a single charmer system such as theDFT-Spread OFDM but may be a multicarrier system such as the OFDM.

The scheduling unit 203 performs scheduling for mapping the user data inrespective channels of the uplink based on CQI information supplied bythe channel estimation unit 208 described later and schedulinginformation supplied by an upper layer. The signature selection unit 204selects a signature ID number to be used in a random access inaccordance with an instruction issued by the upper layer. Then, thesignature selection unit 204 outputs the selected signature ID number tothe preamble generation unit 205.

The preamble generation unit 205 generates a preamble by using thesignature ID number selected by the signature selection unit 204 andoutputs the generated preamble to the DFT-S-OFDM modulation unit 202.The synchronization correction unit 206 determines transmission timingon the basis of synchronization information input from the control dataextraction unit 210 and outputs data modulated in accordance with thetransmission timing to the radio unit 207.

The radio unit 207 upconverts the modulated data to a radio frequencyand transmits the resultant to the base station 100. Furthermore, theradio unit 207 receives downlink data from the base station 100,downconverts the received data to a base band signal, and outputs thereceived data to the OFDM demodulation unit 209. The channel estimationunit 208 estimates a radio propagation path characteristic on the basisof a downlink pilot channel and outputs the obtained estimation resultto the OFDM demodulation unit 209. Furthermore, the channel estimationunit 208 converts the estimation result to CQI information for informingthe base station 100 of the estimation result of the radio propagationpath and outputs the CQI information to the scheduling unit 203.

The OFDM demodulation unit 209 demodulates the received data input fromthe radio unit 207 in accordance with the estimation result of the radiopropagation path input from the channel estimation unit 208. The controldata extraction unit 210 separates the received data to user data andcontrol data. Then, the control data extraction unit 210 outputsscheduling information included in the separated control data to thescheduling unit 203, outputs synchronization information of the uplinkto the synchronization correction unit 206 and outputs the remainingcontrol data and the user data to the upper layer.

The mobile station 200 having the aforementioned configuration iscontrolled by the upper layer so as to execute the processing throughthe procedures illustrated in FIGS. 3 through 7 and FIG. 10 describedlater.

Next, an operation performed, in the communication system including thebase station 100 and the mobile station 200 having the aforementionedconfigurations, for resuming downlink data transmission to the mobilestation 200 out of uplink synchronization will be described withreference to FIGS. 3 through 5 .

FIG. 3 is a sequence chart illustrating an operation performed when thebase station 100 of this embodiment transmits a dedicated signature byusing a DL-SCH and the mobile station 200 succeeds in the CRC of theDL-SCH. FIG. 4 is a sequence chart illustrating an operation performedwhen the base station 100 of this embodiment transmits a dedicatedsignature by using a DL-SCH and the mobile station 200 fails in the CRCof the DL-SCH. FIG. 5 is a sequence chart illustrating an operationperformed when the base station 100 of this embodiment does not transmita dedicated signature by using a DL-SCH.

First, the operation performed when the base station 100 of thisembodiment transmits a dedicated signature by using a DL-SCH and themobile station 200 succeeds in the CRC of the DL-SCH will be describedwith reference to FIG. 3 . The base station 100 manages the uplinksynchronization of the mobile station 200. For example, a timer is set,and when a state where uplink transmission is not performed or a statewhere uplink synchronization information is not updated has continuedfor a given period of time, it is determined that “the mobile station200 is out of uplink synchronization”. Similarly, the mobile station 200also manages the uplink synchronization.

When the base station 100 detects arrival of data for the mobile station200 out of uplink synchronization (ST301), it transmits downlinkresource allocation and downlink data (ST302 and ST304). At this point,the downlink resource allocation is transmitted by using an L1/L2control channel and the downlink data is transmitted by using adownlink-shared channel DL-SCH. It is noted that the DL-SCH includesinformation for specifying a dedicated signature.

When the mobile station 200 receives the downlink resource allocationand the downlink data, it performs the CRC of the L1/L2 control channeland the DL-SCH. In this exemplary case, the mobile station 200 detectssuccess in the CRC of both the channels (ST303 and ST305). Then, whenthe mobile station 200 detects the downlink resource allocation and thededicated signature, it transmits a preamble of a random access channelby using the dedicated signature (ST306: Message 1).

When the base station 100 detects the dedicated signature by using therandom access channel, it transmits a preamble response (ST307: Message2). In this exemplary case, the base station 100 can specify the mobilestation 200 through the detection of the dedicated signature andspecifies C-RNTI, that is, identification information of the mobilestation 200.

The preamble response includes the L1/L2 control channel and the DL-SCH.The L1/L2 control channel includes RA-RNTI used for identifying thepreamble response or C-RNTI used for directly specifying the mobilestation 200. The DL-SCH includes synchronization information. When theRA-RNTI is used, the DL-SCH includes the dedicated signature or theC-RNTI.

After transmitting the preamble response, the base station 100subsequently resumes general data transmission (ST308 and ST309). Whenthe base station 100 transmits the dedicated signature by using a DL-SCHand the mobile station 200 succeeds in the CRC of the DL-SCH, theoperation for resuming downlink data transmission to the mobile station200 out of uplink synchronization is performed in this manner.

Incidentally, the downlink data transmitted in ST304, the preambleresponse transmitted in ST307 and the downlink data transmitted in ST309may include user data having arrived at the base station 100. In thiscase, the preamble transmit ted in ST306 functions as HARQ ACK of thedownlink data transmitted in ST304.

Next, the operation performed when the base station 100 transmits adedicated signature by using a DL-SCH and the mobile station 200 failsin the CRC of the DL-SCH will be described with reference to FIG. 4 . Asdescribed with reference to FIG. 3 , the base station 100 manages theuplink synchronization of the mobile station 200. Similarly, the mobilestation 200 also manages the uplink synchronization.

When the base station 100 detects arrival of data for the mobile station200′ out of uplink synchronization (ST401), it transmits downlinkresource allocation and downlink data (ST402 and ST404). At this point,the downlink resource allocation is transmitted by using an L1/L2control channel and the downlink data is transmitted by using adownlink-shared channel DL-SCH. It is noted that the DL-SCH includesinformation for specifying a dedicated signature.

When the mobile station 200 receives the downlink resource allocationand the downlink data, it performs the CRC of the L1/L2 control channeland the DL-SCH. In this exemplary case, the mobile station 200 detectssuccess in the CPC of the former channel but detects fail in the CRC ofthe latter channel (ST403 and ST405) Then, when the mobile station 200detects the downlink resource allocation, it transmits a preamble of arandom access channel by using a signature randomly selected (ST406:Message 1).

When the base station 100 detects the signature by using the randomaccess channel, it transmits a preamble response (ST407: Message 2). Inthis exemplary case, the base station 100 cannot specify the mobilestation 200 through the detection of the signature. The preambleresponse includes the L1/L2 control channel and the DL-SCH. The L1/L2control channel includes RA-RNTI used for identifying the preambleresponse. The DL-SCH includes mapping information for synchronizationinformation and a signature, mapping information for the signature andnew C-RNTI (T-C-RNTI) and scheduling information for Message 3. At thispoint, the base station 100 cannot grasp the reason why the mobilestation 200 has performed the random access.

When the mobile station 200 receives the preamble response, it transmitsMessage 3 in accordance with the scheduling information for Message 3(ST408: Message 3). Message 3 includes C-RNTI. When the base station 100receives the C-RNTI, it detects that the message is a response from themobile station 200 specified by the downlink resource allocationtransmitted in ST402 and the downlink data transmitted in ST404.

Furthermore, when the base station 100 receives Message 3, it transmitscontention resolution as contention resolution information to be usedwhen a plurality of mobile stations 200 simultaneously performtransmission by using the same signature in the preamble transmitted inST406 (ST409: Message 4). The L1/L2 control channel or Message 4includes the T-C-RNTI specified by the base station 100 in Message 2,and the DL-SCH includes mobile station identification informationdetected by the base station 100 in Message 3.

After transmitting the contention resolution, the base station 100subsequently resumes general data transmission (ST410 and ST411). Whenthe base station 100 transmits a dedicated signature by using a DL-SCHand the mobile station 200 fails in the CRC of the DL-SCH, the operationfor resuming downlink data transmission to the mobile station 200 out ofuplink synchronization is performed in this manner.

Incidentally, the downlink data transmitted in ST404 may include userdata having arrived at the base station 100. When the user data is thusincluded, the HARQ may be employed for the downlink data transmitted inST404 and the downlink data transmitted in ST411. In this case, Message3 transmitted in ST408 functions as HARQ MACK of the downlink datatransmitted in ST404.

The aforementioned operation performed in the communication system issimilarly executed also when the base station 100 does not transmit adedicated signature by using a DL-SCH and the mobile station 200 failsin the CRC of the DL-SCH.

Next, the operation performed when the base station 100 does nottransmit a dedicated signature by using a DL-SCH and the mobile station200 succeeds in the CRC of the DL-SCH will be described with referenceto FIG. 5 . As described with reference to FIGS. 3 and 4 , the basestation 100 manages the uplink synchronization of the mobile station200. Similarly, the mobile station 200 also manages the uplinksynchronization.

When the base station 100 detects arrival of data for the mobile station200 out of uplink synchronization (ST501), it transmits downlinkresource allocation and downlink data (ST502 and ST504). At this point,the downlink resource allocation is transmitted by using an L1/L2control channel and the downlink data is transmitted by using adownlink-shared channel DL-SCH.

It is noted that the DL-SCH includes information indicating that nodedicated signature is allocated in resuming the downlink datatransmission. The information indicating that no dedicated signature isallocated may be not only addition of information but also detection bythe mobile station 200 of no dedicated signature included in the data orof a signature not reserved as a dedicated signature included in thedata.

When the mobile station 200 receives the downlink resource allocationand the downlink data, it performs the CRC of the L1/L2 control channeland the DL-SCH. In this exemplary case, the mobile station 200 detectssuccess in the CRC of both the channels (ST503 and ST505). Then, whenthe mobile station 200 detects the downlink resource allocation and theinformation indicating that no dedicated signature is allocated, ittransmits a preamble of a random access channel by using a signaturerandomly selected (ST506: Message 1).

When the base station 100 detects the signature by using a random accesschannel, it transmits a preamble response (ST507: Message 2). In thiscase, the base station 100 cannot specify the mobile station 200 throughthe detection of the signature. The preamble response includes the L1/L2control channel and the DL-SCH. The L1/L2 control channel includesRA-RNTI used for identifying the preamble response. The DT-CCH includesmapping information for synchronization information and a signature,mapping information for the signature and new C-RNTI (T-C-RNTI) andscheduling information for Message 3. At this point, the base station100 cannot grasp the reason why the mobile station 200 has performed therandom access.

When the mobile station 200 receives the preamble response, it transmitsMessage 3 in accordance with the scheduling information for Message 3(ST508: Message 3). Message 3 includes C-RNTI. When the base station 100receives the C-RNTI, it detects that the message is a response from themobile station 200 specified by the downlink resource allocationtransmitted in ST502 and the downlink data transmitted in ST504.

Furthermore, when the base station 100 receives Message 3, it transmitscontention resolution as contention resolution information to be usedwhen a plurality of mobile stations 200 simultaneously performtransmission by using the same signature in the preamble transmitted inST506 (ST509: Message 4). The L1/L2 control channel of Message 4includes the T-C-RNTI specified by the base station 100 in Message 2,and the DL-SCH includes mobile station identification informationdetected by the base station 100 in Message 3.

After transmitting the contention resolution, the base station 100subsequently resumes general data transmission (ST510 and ST511). Whenthe base station 100 does not transmit a dedicated signature by using aDL-SCH and the mobile station 200 succeeds in the CRC of the DL-SCH, theoperation for resuming downlink data transmission to the mobile station200 out of uplink synchronization is performed in this manner.

Incidentally, the downlink data transmitted in ST504 may include userdata having arrived at the base station 100. When the user data is thusincluded, the HARQ may be employed for the downlink data transmitted inST504 and the downlink data transmitted in ST511. In this case, Message3 transmitted in ST508 functions as HARQ ACK or NACK.

The aforementioned operation performed in the communication system issimilarly executed when the base station 100 does not transmit adedicated signature by using a DL-SCH and the mobile station 200 failsin the CRC of the DL-SCH.

As described with reference to FIGS. 4 and 5 , when the base station 100transmits neither a dedicated signature by using a DL-SCH nor downlinkdata, the same operation is executed no matter whether the mobilestation 200 succeeds or fails in the CRC of the DL-SCH. In other words,the transmission of the DL-SCH may be omitted in such a case.

Accordingly, as an alternative operation, the base station 100 does nottransmit the downlink data in ST404 or ST504 so that the mobile station200 can always fail in the CRC. Thus, the mobile station 200 can beinformed of allocation of no dedicated signature without using thedownlink resource. Now, an operation for resuming the downlink datatransmission to the mobile station 200 out of uplink synchronizationperformed in this case will be described with reference to FIG. 6 .

As illustrated in FIG. 6 , when the base station 100 detects arrival ofdata for the mobile station 200 out of uplink synchronization (ST601),it transmits downlink resource allocation (ST602). At this point, thedownlink resource allocation is transmitted by using an L1/L2 controlchannel. It is noted that no downlink data is transmitted.

When the mobile station 200 receives the downlink resource allocation,it performs the CRC of the L1/L2 control channel and the DL-SCH. In thisexemplary case, the mobile station 200 detects success in the CRC of theformer channel but detects fail in the CRC of the latter channel (ST603and ST604). Then, when the mobile station 200 detects the downlinkresource allocation, it transmits a preamble of a random access channelby using a signature randomly selected (ST605: Message 1). Naturally,since a dedicated signature is not included in the DL-SCH, the mobilestation 200 does not perform the CRC of the DL-SCH, and when it detectsthe downlink resource allocation (ST603), it transmits a preamble arandom access channel by using a signature randomly selected (ST605).

Furthermore, the L1/L2 control channel is a channel used also fortransmitting uplink resource allocation. In general, the mobile station200 having received uplink resource allocation transmits a UL-SCH. Themobile station 200 out of uplink synchronization, however, similarlyperforms a contention base random access when it detects the uplinkresource allocation. In other words, the mobile station 200 out ofuplink synchronization perform a random access when it detects anyresource allocation (uplink or downlink resource allocation). Theresource allocation herein includes allocation for persistent scheduling(allocated by specifying a frequency and a time area using a signal ofthe upper layer). Thus, the base station 100 can instruct the mobilestation 200 to perform a random access through a simple operation.

When the base station 100 detects a signature by using a random accesschannel, it transmits a preamble response (ST606: Message 2). The basestation 100 cannot specify the mobile station 200 through detection ofthe signature. The preamble response includes the L1/L2 control channeland the DL-SCH. The L1/L2 control channel includes RA-RNTI used foridentifying the preamble response. The DL-SCH includes mappinginformation for synchronization information and a signature, mappinginformation for the signature and new C-RNTI (T-C-RNTI) and schedulinginformation for Message 3. At this point, the base station 100 cannotgrasp the reason why the mobile station 200 has performed the randomaccess.

When the mobile station 200 receives the preamble response, it transmitsMessage 3 in accordance with the scheduling information for Message 3(ST607: Message 3). Message 3 includes C-RNTI. When the base station 100receives the C-RNTI, it detects that the message is a response from themobile station 200 specified by the downlink resource allocationtransmitted in ST602.

Furthermore, when the base station 100 receives Message 3, it transmitscontention resolution as contention resolution information to be usedwhen a plurality of mobile stations 200 simultaneously performtransmission by using the same signature in the preamble transmitted inST605 (ST608: Message 4). The L1/L2 control channel of Message 4includes the T-C-RNTI specified by the base station 100 in Message 2,and the DL-SCH includes mobile station identification informationdetected by the base station 100 in Message 3.

After transmitting the contention resolution, the base station 100subsequently resumes general data transmission (ST609 and ST610). Whenthe base station 100 omits the transmission of the DL-SCH, the operationfor resuming downlink data transmission to the mobile station 200 out ofuplink synchronization is performed in this manner.

At this point, an operation performed when the mobile station 200 ofthis embodiment fails in the CRC of the L1/L2 control channel will bedescribed with reference to FIG. 7 . As described with reference toFIGS. 3 through 5 , the base station 100 manages the uplinksynchronization of the station 200. Similarly, the mobile station 200also manages the uplink synchronization.

When the base station 100 detects arrival of data for the mobile station200 out of uplink synchronization (ST701) it transmits downlink resourceallocation and downlink data (ST702 and ST704). At this point, thedownlink resource allocation is transmitted by using an L1/L2 controlchannel and the downlink data is transmitted by using a downlink-haredchannel DL-SCH.

When the mobile station 200 receives the downlink resource allocationand the downlink data, it performs the CRC of the L1/L2 control channeland the DL-SCH. In this exemplary case, the mobile station 200 detectsfail in the CRC of both the channels (ST703 and ST705). Since thedownlink resource allocation cannot be detected, the mobile station 200halts receiving until the next receiving cycle, so as to receive theL1/L2 control channel again.

When the base station 100 does not receive a response from the mobilestation 200 within a prescribed window time (whereas the response ismade by different methods depending upon the aforementioned situationsdescribed with reference to FIGS. 4 through 6 ), it detects that themobile station 200 could not receive the downlink resource allocation(ST706). Then, when the base station 100 detects that the mobile station200 could not receive the data, it waits for the next transmittingcycle, so as perform the operation for resuming the downlink datatransmission to the mobile station 200 out of uplink synchronizationagain (ST707 and ST708).

In this manner, in the communication system of this embodiment, variousoperations are precedently prepared in accordance with situations ofallocating a dedicated signature by the base station 100, and therefore,downlink data transmission can be efficiently resumed no matter whethera dedicated signature can be allocated.

Now, an operation performed by the base station 100 of this embodimentfor resuming downlink data transmission to the mobile station 200 out ofuplink synchronization be described. FIG. 8 is a flowchart used forexplaining an operation performed by the base station 100 of thisembodiment for resuming downlink data transmission to the mobile station200 out of uplink synchronization.

As illustrated in FIG. 8 , when the base station 100 detects resume ofdownlink data transmission (ST801), it checks the uplink synchronizationof the mobile station 200 (ST802). When the mobile station 200 is notout of uplink synchronization, the base station 100 performs generaldata transmission (ST810). On the other hand, when the mobile station200 out of uplink synchronization, the base station 100 checks whetheror not a dedicated signature can be allocated (ST803).

At this point, when a dedicated signature can be allocated, the basestation 100 selects a dedicated signature (ST804), and transmitsdownlink resource allocation and downlink data to the mobile station 200(ST805 and ST806). The downlink data includes the dedicated signature.

On the other hand, when a dedicated signature cannot be allocated, thebase station 100 transmits at least downlink resource allocation to themobile station 200 (ST807). Then, the base station 100 transmits, to themobile station 200, downlink data including information indicating thatno dedicated signature is allocated or transmits no downlink data(ST808). After transmitting the downlink data in ST806 or the like, thebase station 100 determines whether or not a response is received fromthe mobile station 200 within a prescribed window time (ST809). When theresponse is not received, the processing returns to ST803, so that thebase station 100 can execute the processing of and after ST803.

Next, an operation performed by the base station 100 of this embodimentfor random access control will be described. FIG. 9 is a flowchart usedfor explaining the operation performed by the base station 100 of thisembodiment for the random access control.

As illustrated in FIG. 9 , when the base station 100 receives a preambleby using a random access channel (ST901), it checks whether or not thepreamble is a dedicated signature (ST902). At this point, when thepreamble is a dedicated signature, the base station 100 transmits apreamble response (ST903) and continues data transmission (ST909).

On the other hand, when the preamble is not a dedicated signature, thebase station 100 transmits a preamble response including schedulinginformation for Message 3 (ST904) and starts processing for receivingMessage 3. When Message 3 is received (ST905), the base station 100checks whether or not Message 3 includes C-RNTI of the mobile station200 for resuming downlink data transmission (ST906).

At this point, when C-RNTI of a mobile station 200 other than the mobilestation 200 corresponding to the target of the resume of downlink datatransmission or another ID is detected, random access processing derivedfrom another cause is performed (ST907). On the contrary, when theC-RNTI of the mobile station 200 corresponding to the target of theresume of downlink data transmission is detected, the base station 100transmits contention resolution to the mobile station 200 (ST908) andcontinues the data transmission (ST909).

Next, an operation performed by the mobile station 200 of thisembodiment out of uplink synchronization for resuming downlink datatransmission will be described. FIG. 10 is a flowchart used forexplaining the operation performed by the mobile station 200 of thisembodiment out of uplink synchronization for resuming downlink datatransmission.

Illustrated in FIG. 10 , when the mobile station 200 detects its ownC-RNTI by using an L1/L2 control channel (ST1001), it checks uplinksynchronization (ST1002). When the mobile station 200 is not out ofuplink synchronization, it performs general data receipt (ST1012). Onthe other hand, when the mobile station 200 is out of uplinksynchronization, it receives downlink data (ST1003) and determineswhether or not the CRC has succeeded (ST1004).

When the CRC has failed, the mobile station 200 transmits a preamble byusing a signature randomly selected (ST1005). Naturally, if a dedicatedsignature is not included in a DL-SCH, when the mobile station 200detects its own C-RNTI by using the L1/L2 control channel (ST1001), itchecks the uplink synchronization. When it is determined that the mobilestation 200 is out of synchronization (ST1012), it transmits a preambleby using a signature randomly selected (ST1005). After transmitting thepreamble by using the signature randomly selected, the mobile station200 receives a preamble response (Message 2) from the base station 100(ST1006).

Then, the mobile station 200 acquires, from the preamble response(Message 2), mapping information for synchronization information and asignature, mapping information for the signature and new C-RNTI(T-C-RNTI) and scheduling information for Message 3, and transmitsMessage 3 including its own C-RNTI (ST1007). After transmitting Message3, the mobile station 200 receives contention resolution (Message 4)from the base station 100 (ST1008). Thereafter, the mobile station 200continues the data receipt (ST1012).

On the other hand, when the CRC has succeeded in ST1004, the mobilestation 200 checks whether or not a dedicated signature is included inthe downlink data (ST1009). Incidentally, when a dedicated signature isnot included, the mobile station 200 transmits a preamble by using asignature randomly selected (ST1005).

When a dedicated signature is included, the mobile station 200 transmitsa preamble by using the dedicated signature (ST1010). After transmittingthe preamble by using the dedicated signature, the mobile station 200receives a preamble response (Message 2) from the base station 100(ST1011). Then, the mobile station 200 acquires the synchronizationinformation from the preamble response (Message 2) and continues thedata receipt (ST1012).

In this manner, in the communication system of this embodiment, themobile station 200 perform a random access by using a differentsignature depending upon the information included in a DL-SCH and thecheck result of the CRC of the DL-SCH, and it is determined whether ornot contention resolution is transmitted by the base station 100depending upon a signature used in the random access before transmittingdownlink data. Therefore, the downlink data transmission can be resumedwhile assuming the occurrence of contention with another mobile station200 depending upon a signature selected by the mobile station 200, andhence, an efficient procedure can be realized for resuming the downlinkdata transmission no matter whether a dedicated signature can beallocated.

Although both the mobile station 200 and the base station 100 manage theuplink synchronization with a timer in the above description of thecommunication system or this embodiment, the invention is applicablealso when the base station 100 detects that the mobile station is out ofuplink synchronization and issues an uplink synchronization request.Now, the case where the base station 100 detects that the mobile station200 is out of uplink synchronization and issues an uplinksynchronization request will be described.

A base station periodically monitors an uplink pilot channel UPiCH froma mobile station so as to generate synchronization information. The basestation detects shift between the arrival time of the uplink pilotchannel and the base time so as to set a value of the shift as thesynchronization information. When the subcarrier is 15 kHz and the OFDMsymbol is 70 microseconds, the granularity of the information of timingshift is, for example, 0.52 microsecond. In general, the uplinksynchronization is kept by periodically transmitting the synchronizationinformation from the base station to the mobile station. When thesynchronization information exceeds the tolerance in keeping the uplinksynchronization, however, the base station determines whether or notuplink resynchronization through a random access is necessary.

FIG. 11 is a sequence chart illustrating an operation performed when thebase station 100 of this embodiment transmits an uplink synchronizationrequest and a dedicated signature for uplink resynchronization(hereinafter referred to as the “dedicated signature”) by using a DL-SCHand the mobile station 200 succeeds in the CRC of the DL-SCH. FIG. 12 isa sequence chart illustrating an operation performed when the basestation 100 of this embodiment transmits an uplink synchronizationrequest by using a DL-SCH and the mobile station 200 fails in the CRC ofthe DL-SCH. FIG. 13 is a sequence chart illustrating an operationperformed when the base station 100 of this embodiment transmits anuplink synchronization request by using a DL-SCH.

First, the operation performed when the base station 100 of thisembodiment transmits an uplink synchronization request and a dedicatedsignature by using a DL-SCH and the mobile station 200 succeeds in theCRC of the DL-SCH will be described with reference to FIG. 11 . The basestation 100 manages the uplink synchronization of the mobile station200. The base station 100 determines whether or not uplinkresynchronization through random access is necessary, for example, onthe basis of the physical properties of the uplink transmitted from themobile station 200.

When the base station 100 determines that the uplink resynchronizationis necessary (ST1101), it transmits downlink resource allocation anddownlink data (ST1102 and ST1104). At this point, the downlink resourceallocation is transmitted by using an L1/L2 control channel and thedownlink data is transmitted by using a downlink-shared channel DL-SCH.It is noted that the DL-SCH includes an uplink synchronization requestand information for specifying a dedicated signature.

When the mobile station 200 receives the downlink resource allocationand the downlink data, it performs the CRC of the L1/L2 control channeland the DL-SCH. In this exemplary case, the mobile station 200 detectssuccess in the CRC of the both channels (ST1103 and ST1105). Then, whenthe mobile station 200 detects the downlink resource allocation, theuplink synchronization request and the dedicated signature by referringto data included in the DL-SCH (ST1106), it performs dedicated signaturerandom access processing by using the dedicated signature (ST1107). Thisprocessing is performed in the same manner as in ST306 and ST307 of FIG.3 . Incidentally, HARQ ACK generally transmitted by using a PUCCH inreceiving a DL-SCH is not transmitted when an uplink synchronizationrequest is detected. When the dedicated signature random accessprocessing is performed, communication of uplink data and downlink datais resumed (ST1108).

Next, the operation performed when the base station 100 transmits anuplink synchronization request by using a DL-SCH and the mobile station200 fails in the CRC of the DL-SCH will be described with reference toFIG. 12 . As described with reference to FIG. 11 , the base station 100manages the uplink synchronization of the mobile station 200.

When the base station 100 determines that the uplink resynchronizationis necessary (ST1201), it transmits downlink resource allocation anddownlink data (ST1202 and ST1204). At this point, the downlink resourceallocation is transmitted by using an L1/L2 control channel and thedownlink data is transmitted by using a downlink-shared channel DL-SCH.It is noted that the DL-SCH includes an uplink synchronization request.

When the mobile station 200 receives the downlink resource allocationand the downlink data, it performs the CRC of the L1/L2 control channeland the DL-SCH. In this exemplary case, the mobile station 200 detectssuccess in the CRC of the former channel but fail in the CRC of thelatter channel (ST1203 and ST1205). Then, when the mobile station 200detects the downlink resource allocation, it transmits HARQ NACK byusing a PUCCH (ST1206). In this case, the NACK is transmitted withouttiming adjustment. Since this signal has low reliability, the basestation 100 transmits an uplink synchronization request again if itwaits for a random access performed by the mobile station 200 and therandom access is not performed.

Since the transmission of the NACK out of synchronization does notfrequently occur and does not seriously affect another mobile station,is acceptable as it is but if it necessary to avoid the transmission ofthe NACK, the following method is employed: The base station 100 adds,to the information of the L1/L2 control channel, information indicationthat NACK is not to be transmitted. For example, the followingarrangement is set with the mobile station 200: Since a DL-SCH used foruplink resynchronization does not use HARQ, an HARQ process numbercorresponding to an information field of the HARQ and one of informationstrings of HARQ Redundancy Version (of, for example, all 0) arereserved, and when the reserved information is included in theinformation field of the HARQ, NACK is not transmitted. Alternative,arrangement that one bit is simply added to an L1/L2 control channel soas not to transmit NACK is set with the mobile station 200. Thus, thebase station 100 can avoid the transmission of NACK from a mobilestation out of synchronization, so as to reduce interference withanother mobile station. When this method is employed, even if the mobilestation does not manage the synchronization with a timer, the mobilestation can detect, receiving an L1/L2 control channel, that it is aDL-SCH for uplink resynchronization. In other words when an L1/L2control channel is received, the mobile station can perform a contentionbase random access by failing in the CRC of the DL-SCH.

Next, the operation performed when the base station 100 transmits anuplink synchronization request by using a DL-SCH will be described withreference to FIG. 13 . As described with reference to FIGS. 11 and 12 ,the base station 100 manages the uplink synchronization of the mobilestation 200.

When the base station 100 determines that uplink resynchronization isnecessary (ST1301), it transmits downlink resource allocation anddownlink data (ST1302 and ST1304). At this point, the downlink resourceallocation is transmitted by using an L1/L2 control channel and thedownlink data is transmitted by using a downlink-shared channel DL-SCH.

It is noted that the DL-SCH includes information that no dedicatedsignature is allocated in the uplink resynchronization. The informationindicating that no dedicated signature is allocated may be not onlyaddition of information but also detection by the mobile station 200 ofno dedicated signature included in the data or of a signature notreserved as a dedicated signature included in the data.

When the mobile station 200 receives the downlink resource allocationand the downlink data, it performs the CRC of the L1/L2 control channeland the DL-SCH. In this exemplary case, the mobile station 200 detectssuccess in the CRC of both the channels (ST1303 and ST1305). Then, whenthe mobile station 200 detects the downlink resource allocation, uplinksynchronization request and the information of no dedicated signature(ST1306), it performs contention base random access processing by usinga signature randomly selected (ST1307). This processing is performed inthe same manner as in ST506 through ST509 of FIG. 5 . Incidentally, HARQACK generally transmitted by using a PUCCH in receiving DL-SCH is nottransmitted when an uplink synchronization request is detected. When thecontention base random access processing is performed, communication ofuplink data and downlink data is resumed (ST1308).

Next, an operation performed by the mobile station 200 of thisembodiment for uplink resynchronization will be described. FIG. 14 is aflowchart used for explaining the operation performed by the mobilestation 200 of this embodiment for the uplink resynchronization.

As illustrated in FIG. 14 , when the mobile station 200 detects its ownC-RNTI by using an L1/L2 control channel (ST1401), it receives downlinkdata (ST1042) and determines whether or not the CRC has succeeded(ST1403).

At this point, when the mobile station 200 has failed in the CRC, ittransmits HARQ NACK (ST1404). When information of the L1/L2 controlchannel includes information that NACK is not to be transmitted, themobile station 200 does not transmit the NACK. When the mobile station200 has succeeded in the CRC, it checks whether or not an uplinksynchronization request is included in the data (ST1405). When an uplinksynchronization request is not included, the mobile station 200transmits HARQ ACK (ST1406). When an uplink synchronization request isincluded, the mobile station 200 further checks whether or not adedicated signature is included in the downlink data (ST1407).

At this point, when a dedicated signature is not included, the mobilestation 200 transmits a preamble by using a signature randomly selected(ST1408). After transmitting the preamble by using the randomly selectedsignature, the mobile station 200 receives a preamble response (Message2) from the base station 100 (ST1409). Then, the mobile station 200acquires, from the preamble response (Message 2), mapping informationfor synchronization information and a signature, mapping information forthe signature and new C-RNTI (T-C-RNTI) and scheduling information forMessage 3, and transmits Message 3 including its own C-RNTI (ST1410).After transmitting Message 3, the mobile station 200 receives contentionresolution (Message 4) from the base station 100 (ST1411). Thereafter,the mobile station 200 continues data transmission/receipt (ST1412).

On the other hand, when a dedicated signature is determined to beincluded in ST1407, the mobile station 200 transmits a preamble by usingthe dedicated signature (ST1413). After transmitting the preamble byusing the dedicated signature, the mobile station 200 receives apreamble response (Message 2) from the base station (ST1414). Then, themobile station 200 acquires synchronization information from thepreamble response (Message 2) and continues data transmission/receipt(ST1412).

Now, an operation performed when the continuation of uplinksynchronization is managed with timer as described above and anoperation performed when an uplink synchronization request is receivedfrom the base station 100 will be described with reference to FIG. 15 .FIG. 15 is a flowchart used for explaining the operations performed bythe mobile station 200 of this embodiment when the continuation ofuplink synchronization is managed with a timer and when an uplinksynchronization request is received from the base station 100. It isnoted that like reference numerals are used in FIG. 15 to refer to likesteps illustrated in FIGS. 10 and 14 so as to omit the description.

As illustrated in FIG. 15 , when the mobile station 200 detects its ownC-RNTI by an L1/L2 control channel (ST1501), it determines whether ornot a timer used for managing the continuation of uplink synchronizationhas expired (ST1502). When the timer used for managing the continuationof the uplink synchronization has expired, the mobile station 200performs the processing of and after ST1003 illustrated in FIG. 10 . Onthe other hand, when the timer used for managing the continuation of theuplink synchronization has not expired, the mobile station 200 performsthe processing of and after ST1402 illustrated in FIG. 14 .

FIG. 16 is a block diagram illustrating a part of the configuration ofthe upper layer of the mobile station 200 of this embodiment. An uplinksynchronization management unit 1601 manages uplink synchronization onthe basis of a DL-SCH received from the base station 100, and instructsa CRC result discrimination unit 1602 to perform the processingillustrated in FIG. 10 or 14 depending upon whether or not the uplinksynchronization is kept. When a timer used for managing the uplinksynchronization has expired, it instructs to perform the processingillustrated in FIG. 10 , and when not, it instructs to perform theprocessing illustrated in FIG. 14 .

The CRC result discrimination unit 1602 performs the CRC of the DL-SCHand discriminates the result of the check. When the CRC fails and themobile station is out of uplink synchronization, the CRC resultdiscrimination unit 1602 instructs a random access execution unit 1603to execute a contention base random access. In the other case, itinstructs a random access discrimination unit 1604 to determine whetheror not a random access is necessary.

The random access discrimination unit 1604 checks whether or not anuplink synchronization request or a dedicated signature is included inthe DL-SCH, and instructs to transmit HARQ ACK/NACK or instructs therandom access execution unit 1603 to execute a dedicated signaturerandom access or a contention base random access in accordance withinformation included in the DL-SCH. The random access execution unit1603 executes the random access in accordance with the instructionissued by the CRC result discrimination unit 1602 or the random accessdiscrimination unit 1604.

In this manner, in the communication system according to thisembodiment, a DL-SCH including an uplink synchronization request andinformation for specifying a dedicated signature is received, and whenthe CRC of the DL-SCH succeeds, a random access is performed by usingthe dedicated signal, and the base station 100 transmits downlink datawithout transmitting contention resolution. On the other hand, when thereceived DL-SCH includes an uplink synchronization request but does notinclude the information for specifying a dedicated signature, a randomaccess is performed by using a signature randomly selected, and the basestation 100 transmits downlink data after transmitting contentionresolution. Since the mobile station 200 performs a random access when aDL-SCH including an uplink synchronization request is received from thebase station 100 in this manner, even when the mobile station 200 doesnot recognize that it is out of uplink synchronization, uplinkresynchronization can be realized.

Incidentally, being out of uplink synchronization detected on the sideof the base station 100 corresponds to a state where the base station100 determines that it is necessary to attain resynchronization with themobile station 200 through a random access no matter whether the mobilestation 200 actually out of uplink synchronization.

As described so far, according to the present embodiment, a randomaccess is performed by a mobile station apparatus by using a differentsignature depending upon information included in a DL-SCH and a resultof the CRC of the DL-SCH, and a base station apparatus transmitsdownlink data after determining whether or not contention resolution istransmitted depending upon the signature used in the random access.Therefore, resume of downlink data transmission or uplinkresynchronization can be performed in accordance with a signatureselected by the mobile station apparatus on the assumption of occurrenceof contention with another mobile station apparatus, and hence, anefficient procedure can be realized when the mobile station apparatus isout of uplink synchronization no matter whether a dedicated signaturecan be allocated.

The present invention is not limited to the above-described embodimentbut may be variously modified. In this embodiment, sizes, shapes and thelike of elements illustrated in the accompanying drawings are notparticularly specified but may be appropriately modified as far as theeffects of the invention can be exhibited. It is to be understood thatchanges and variations may be made without departing from the spirit orscope of the invention.

The invention claimed is:
 1. A mobile station apparatus comprising:processing circuitry configured to: select a random access method inresponse to receiving, from a base station apparatus, information thatincludes a signature, and perform a random access according to theselected random access method; wherein the random access according tothe selected random access method is performed by using a dedicatedsignature when the dedicated signature is detected by said mobilestation apparatus as being the signature in the information; and whereinthe random access according to the selected random access method isperformed by using a randomly selected signature when a signature notreserved as a dedicated signature is detected by said mobile stationapparatus as being the signature in the information.
 2. The mobilestation apparatus according to claim 1, wherein the information furtherincludes an uplink synchronization request.
 3. The mobile stationapparatus according to claim 1, wherein the randomly selected signatureis selected by the mobile station apparatus.
 4. The mobile stationapparatus according to claim 1, wherein in the case that the signaturenot reserved as a dedicated signature is included in the information,the information does not include further information, and the signaturenot reserved as a dedicated signature is included in the information inplace of the dedicated signature.
 5. The mobile station apparatusaccording to claim 1, wherein the dedicated signature, the randomlyselected signature and the signature not reserved as a dedicatedsignature stem from a same set of 64 signatures.
 6. The mobile stationapparatus according to claim 1, wherein the signature not reserved as adedicated signature does not define a maximum signature of a set ofsignatures from which the randomly selected signature is randomlyselected.
 7. The mobile station apparatus according to claim 1, whereinthe information is addressed only to the mobile station apparatus. 8.The mobile station apparatus according to claim 1, wherein the signaturein the information is the only signature in the information, and thesignature is the dedicated signature or the signature not reserved as adedicated signature.
 9. A base station apparatus comprising: processingcircuitry configured to transmit to a single mobile station apparatusinformation that includes a signature for requesting the single mobilestation apparatus to select a random access method and to perform arandom access according to the random access method; wherein a dedicatedsignature is set to the signature included in the information whenrequesting the single mobile station apparatus to select the randomaccess method and to perform the random access according to the selectedrandom access method by using the dedicated signature; and wherein asignature not reserved as a dedicated signature is set to the signatureincluded in the information when requesting the single mobile stationapparatus to select the random access method and to perform the randomaccess according to the selected random access method by using arandomly selected signature.
 10. The base station apparatus according toclaim 9, wherein the information further includes an uplinksynchronization request.
 11. The base station apparatus according toclaim 2, wherein the randomly selected signature is selected by thesingle mobile station apparatus.
 12. The base station apparatusaccording to claim 9, wherein in the case that the signature notreserved as a dedicated signature is included in the information, theinformation does not include further information, and the signature notreserved as a dedicated signature is included in the information inplace of the dedicated signature.
 13. The base station apparatusaccording to claim 9, wherein the dedicated signature, the randomlyselected signature and the signature not reserved as a dedicatedsignature each stem from a same set of 64 signatures.
 14. The basestation apparatus according to claim 9, wherein the signature notreserved as a dedicated signature does not define a maximum signature ofa set of signatures from which the randomly selected signature israndomly selected.
 15. The base station apparatus according to claim 2,wherein the information is addressed only to the single mobile stationapparatus.
 16. The base station apparatus according to claim 9, whereinthe signature in the information is the only signature in theinformation, and the signature is the dedicated signature or thesignature not reserved as a dedicated signature.
 17. A method performedby a base station apparatus, the method comprising: transmitting to asingle mobile station apparatus, information that includes a signaturefor requesting the single mobile station apparatus to select a randomaccess method and to perform a random access according to the selectedrandom access method; setting a dedicated signature to the signatureincluded in the information when requesting the single mobile stationapparatus to select the random access method and to perform the randomaccess according to the selected random access method by using thededicated signature; and setting a signature not reserved as a dedicatedsignature to the signature included in the information when requestingthe single mobile station apparatus to select the random access methodand to perform the random access according to the selected random accessmethod by using a randomly selected signature.
 18. A method performed bya mobile station apparatus, the method comprising: selecting a randomaccess method in response to receiving, from a base station apparatus,information that includes a signature, and performing a random accessaccording to the selected random access method, wherein the randomaccess according to the selected random access method is performed byusing a dedicated signature when the dedicated signature is detected bythe mobile station apparatus as being the signature in the information,and wherein the random access according to the selected random accessmethod is performed by using a randomly selected signature when asignature not reserved as a dedicated signature is detected by themobile station apparatus as being the signature in the information.